1. Field of the Invention
The present invention relates to a toner used for an image forming apparatus, such as a copier, facsimile, printer, etc., and a developer containing the toner, a developer container, a process cartridge, an image forming apparatus and an image forming method, which use the toner, developer, developer container, and process cartridge.
2. Description of the Background
Conventionally, electric latent images or magnetic latent images are made visible with a toner in image forming apparatuses by electrophotography, electrostatic recording method, or the like. In the electrophotography, for example, after forming a latent electrostatic image on a photoconductor, the latent electrostatic image is developed with a toner to form a toner image. The toner image is generally transferred to a recording medium such as paper, and then melted by heating so as to be fixed thereon.
In recent years, demand has arisen for toners having various advantageous properties such as small particle diameters for forming high-quality output images and improved low-temperature fixing ability for energy saving.
Toners obtained by the conventional kneading-pulverizing method are not easily made to have a small particle diameter. In addition, their shape is amorphous and their particle size distribution is broad. Furthermore, these toners have various problems such as requiring a large amount of energy for being fixed, and thus energy saving is hard to achieve.
In particular, in the kneading-pulverizing method, cracks occur at the interfaces of a releasing agent (wax) during pulverization, resulting in that the releasing agent exists on the toner surface in a large amount. As a result, although the releasing effects for fixation can be obtained, toner adhesion to a carrier, a photoconductor and a blade is likely to occur. The properties of such toners are not satisfactory in terms of the image forming process.
In order to overcome the above-described problems the kneading-pulverizing method has, there is proposed a method for producing a toner by the polymerization method. According to the polymerization method, toners are made easily to have a small particle diameter. Their particle size distribution is sharper than that of the toners obtained by the pulverizing method. Furthermore, the wax can be incorporated in the toner particles.
In such polymerization method, improvement of low temperature fixing ability is desired for energy saving. Moreover, according to the improvement of the low temperature fixing ability, it is desired not to impair the heat resistant storage stability and hot offset resistance of toner. To these problems, it is attempt to use, as a binder resin of the toner, polyester resins having excellent low temperature fixing ability and relatively favorable heat resistant storage stability, instead of conventionally used styrene-acrylic resins.
Moreover, Japanese Patent Application Laid-Open (JP-A) No. 2005-15589 discloses use of a crystalline polyester dispersion liquid for introduction of a crystalline polyester in a toner. Since the crystalline polyester resin contained in the toner has crystallinity, the resultant toner has thermofusion properties that the viscosity of the toner dramatically decreases at around the fixing onset temperature (fusion onset temperature). Specifically, the toner has the desirable heat resistant storage stability just below the fusion onset temperature because of the crystallinity, and shows dramatic viscosity reduction (sharp melt) at the fusion onset temperature so as to be fixed. Thus, the toner having both excellent heat resistant storage stability and low temperature fixing ability can be designed. Moreover, such the toner has also excellent releasing width (i.e. difference between the minimum fixing temperature and hot offset occurring temperature).
JP-A No. 2005-15589 discloses that, as a method of producing a crystalline polyester dispersion liquid, a crystalline polyester alone is mixed in a solvent, and then heated and cooled to produce a coarse dispersion liquid, followed by pulverizing the crystalline polyester contained in the produced coarse dispersion liquid with a mechanical pulverization device, to thereby obtain a crystalline polyester dispersion liquid having a volume average particle diameter of 0.2 μm to 1 μm, which is suitably used for toner.
However, it is difficult for the crystalline polyester resin to be dispersed to have a sharp particle size distribution by the method for producing a crystalline polyester dispersion liquid disclosed in JP-A No. 2005-15589. Consequently, the particle size distribution of the toner becomes poor.
On the other hand, the inventors of the present invention have intensively studied a toner in which the crystalline polyester resin is contained, and found that a toner having a small particle diameter tends to have excellent low temperature fixing ability, but poor heat resistant storage stability, and a toner having a large particle diameter tends to have excellent heat resistant storage stability, but poor low temperature fixing ability, in the particle size distribution of the toner. Thus, even though the toner containing the crystalline polyester resin has a particle size distribution to some extend, it is considered that the amount of the crystalline polyester resin to be contained needs to be optimized depending on the particle size distribution, so that the toner has stable and suitable heat resistant storage stability and low temperature fixing ability as a whole.